I know the cube route of sod all about GSHP as such but, from what you have written, I think you might be wise to investigate how deep in the ground the loops have been buried. I say this as it sounds as though the difference in the water temperature and the ground’s surface are minimal whereas there should be a marked difference as the ground should not be chilling as your loop suggests it is. Just my £0.1 worth. Toodles.

Hi, 

I don't claim to be an expert but I do have a GSHP and happy to share my experience. Firstly yes, 50kWh to maintain 17C sounds pretty inefficient. I can heat our old stone walled cottage to a constant 22 - 23C (yes, I know, but it's a holiday let and that's what paying guests seem to expect!) for about 40 - 50kWh during the recent cold snap. But you don't say anything about your house - heat emitters? insulation? Etc i.e. it should well be factors or 5 than the heat pump itself causing the poor performance.

The behind temps look OK 'ish: you should be seeing about 4C difference between in and out. For comparison last Sunday I was seeing:

Brine in: 5.5C

Brine out: 1.3C

Outside air temp: 11CC

Heat out: 39.1C

Heat In: 36.3C

So, not that dissimilar to what you were seeing, which makes me think it might be more to do with your building fabric? We have insulated floor slabs with underfloor heating, oversized radiators upstairs, lime/hemp insulated walls, sheeps wool in the loft, lots of draught proofing and double glazing throughout...

@toodles Thanks - Yeah we had wondered. We don't have any of the technical drawings or calculations of the brine circuit. However we do know that the circuit is nearly 20 years old. Our understanding from reading is that we'd expect the brine circuit to be at a higher temp generally. However without the calculations its a bit difficult to understand the design of the brine circuit..

@graham-s Really useful to know, thank you. We have cavity wall insulation, suspended ground floor with no insultation, double glazing etc. however we aren't sure what the speciation of the system is designed for (in terms of heat loss). Our main concern is the buffer tank as it really not holding the heat and heating circuit seems to be lower than the set point of the buffer tank..

We have a small gshp, and in very cold weather the glycol out can be 0C, sometimes even -6C by the end of winter in a cold snap.  Our rads run at 32C though, quite a bit more efficient than your buffer at 47C.  It’s that deltaT that predicts the COP generally - attached a graph for our system, for interest.  (Blue is hot water, orange heating).  
How do you know the consumed electricity - ideally a mid certified meter placed in line with the gshp unit.

Do you have an EPC for the property?  That will give estimated yearly energy demand.

Posted by: @didjerama_uk

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@graham-s Really useful to know, thank you. We have cavity wall insulation, suspended ground floor with no insultation, double glazing etc. however we aren't sure what the speciation of the system is designed for (in terms of heat loss). Our main concern is the buffer tank as it really not holding the heat and heating circuit seems to be lower than the set point of the buffer tank..

Is the buffer tank in the house? If so, any heat loss should be contributing to the domestic heating and, for the summer half the heat should be making the house too hot. Do you need the buffer tank to be that hot?

@johnr Thanks - the Buffer tank is in the integral garage. We need the buffer tank to be that hot otherwise the house doesn't heat up. We have tried the buffer tank at a lower set point however it seems to make things worse.

Once you have 3-5 degree delta t on brine side then that’s all that’s matters on the collector side.

If you are low on gas or poor antifreeze, you’ll get low pressure faults. Once you don’t get those, then just focus on the hot side. That’s where the money is saved 

What matters on the heating and hot water is you just keep your flow temps down as low as possible.